1. I did my first starter this past Sunday with the intentions of brewing yesterday. I wasn't able to brew yesterday as some things came up. How long is my starter going to keep? I put it in the fridge last night since the next time i'll be able to brew will be Saturday morning.

2. How long do you guys leave your stir plate on for? I was afraid I was going to aerate my starter to much (oxidation), so I had it on for 7 hours and then turned it off. Then on monday morning I turned it on for 15 minutes while I got ready for work. I figured it wouldnt be a big deal as some aeration is better then none, but I was wondering for next time if I should just leave it on for the whole fermentation process or do what I did this time.

leave the stir plate on for the full fermentation of the starter (24-48 hours). The whole idea is to oxidize the starter. Yeast like oxygen. It helps them reproduce.

After it's done fermenting you can store it in the fridge but not forever. Use it within a few days ideally. More then a week and it's gonna start to loose some viability. After a few weeks you should probably make a new starter for your old starter.